This study compared the effects of repeated-sprint versus high-intensity intermittent training on performance and post-exercise parasympathetic reactivation in trained male adolescents. Ss were divided into two groups that performed nine weeks of either repeated-sprint training (repeated all-out 6-second shuttle sprints; 14-20 seconds of recovery; N = 8) or high-intensity intermittent training (15- to 20-second runs at 95% of the velocity reached at the end of an intermittent fitness test; 15-20 seconds of recovery; N = 7). Groups performed intervals twice per week and maintained similar external training programs. Before and after training, performance was assessed by the intermittent fitness test, countermovement jump, 10-m sprint time, mean repeated-sprint ability time, and heart rate level during a 6-minute submaximal (60% fitness test velocity) exercise test (where parasympathetic reactivation was assessed during the recovery phase).

Parasympathetic function, fitness test velocity, and mean repeated-sprint ability time were improved with high-intensity intermittent training but not repeated-sprint training. In contrast, changes in countermovement jump and heart rate were similar in both groups.

Implication. High-intensity intermittent training was more effective than repeated-sprint training for improving post-exercise parasympathetic function and physical performance in adolescent males. [There is a suggestion in this study that "sprint work" needs to be of a certain duration, such as in the 15-20 seconds range, as opposed to a very short ~6 seconds range.]